After a few individual trailer reveals, Ubisoft unveils the relationships in Splinter Cell Blacklist, describing the Fourth Echelon as a 'family.' Although they are all highly trained, highly specialized individuals in the team, the relationship dynamics plays out so that everyone approximates traditional family roles one way or another.
Of course, Sam Fisher is Fourth Echelon's father figure. He's the leader of the pack, the one who calls the shots and has final say. Sam has to struggle with the change in circumstances, being assigned all the responsibility her previously didn't have to deal with, and more immediately, having to deal with being part of the team.
As you may have guessed, Anna Grímsdóttir, would be the mother, but the Grim Ice Queen is hardly ideal for the role. In the events of prior games, she and Sam already called it quits, so their relationship is strained from the onset. Anna and Sam have a complicated history, but she also thinks she should be in charge of Fourth Echelon.
Charlie Cole, as we covered here before, is Fourth Echelon's tech expert, and really helps round up the team as the son. He looks up to Sam, Sam brings him in to Fourth Echelon. Charlie is eager to please Sam, even if it means bending the rules, and so this leads to friction between him and Anna, a believable family relationship if not a great one. Later in the game, Anna will later warm up to Sam, and even help him clean up his messes behind Sam's back, like a real mother would.
On the flip side, Isaac Briggs is brought in by Grim, intended to be Sam's partner, to accompany him in the missions. Briggs is everything Anna wishes Sam was, and his presence really drives home to Sam the concept that he now works in a team. His changing relationship with Briggs, as he grows to trust and share more tasks with him, will also lead to a change in Sam himself. Ubi didn't really assign him a family role but I would think of him as Anna's favored son.
Finally, there is Andriy Kobin, the black sheep of the family. Andriy is a bad guy through and through, and works with Sam to further his own interests. Sam needs Andriy for his intel, and Andriy needs Sam to pursue his own vendettas.
This paradigm of the Fourth Echelon as a family serves to frame the characters and their personal growth through the game. It does seem that this Splinter Cell will get more cinematic narrative as a result, but that may not be a bad thing.
Source: Ubisoft Blog